Method and device for controlling a variable valve train of an internal combustion engine

Abstract

A method for controlling a variable valve train of an internal combustion engine including multiple cylinders is disclosed. At a first operating point of the engine, an intake air amount is determined and cylinder-individual values for a fuel amount reduction are determined by successively reducing the respectively supplied fuel amount for each cylinder until a characteristic representing uneven running of the engine has reached a predetermined uneven running threshold value. A ratio of a change in the intake valve lift to the resulting change in the intake air amount is determined for the first operating point. Cylinder-individual deviations of the intake valve lift from a reference value are determined based on the ratio, the intake air amount at the first operating point, and the associated value for the fuel amount reduction. The variable valve train is then controlled on the basis of the cylinder-individual deviations of the intake valve lift.

What is claimed is: 
     
       1. A method for controlling a variable valve train of an internal combustion engine with a plurality of cylinders, comprising:
 determining an intake air quantity at a first operating point of the internal combustion engine, 
 at the first operating point, determining cylinder-specific values for a reduction of the fuel quantity by successively reducing the respective delivered quantity of fuel for each cylinder until a parameter representing the uneven running of the internal combustion engine has reached a specified uneven running limit value, 
 determining a ratio of a change of the inlet valve lift to a resulting change of the intake air quantity for the first operating point, 
 determining cylinder-specific deviations of the inlet valve lift from a valve reference value based on the ratio, the intake air quantity at the first operating point, and the associated fuel quantity reduction value, and 
 controlling the variable valve train based on at least one of the cylinder-specific deviations of the inlet valve lift. 
 
     
     
       2. The method of  claim 1 , comprising:
 at a second operating point of the internal combustion engine, at which the inlet valve lift is greater than at the first operating point, determining other cylinder-specific values for a reduction of fuel quantity by successively reducing the respective quantity of fuel delivered for each cylinder until a parameter representing the uneven running of the internal combustion engine has reached a specified uneven running limit value, 
 determining cylinder-specific errors in the fuel delivery based on the other cylinder-specific values for the reduction of fuel quantity and a fuel reference value, and 
 wherein the cylinder-specific errors in the fuel delivery are taken into account during determination of the cylinder-specific values of the reduction of the fuel quantity at the first operating point. 
 
     
     
       3. The method of  claim 1 , wherein the valve train of the internal combustion engine is configured for cylinder-specific control of the lift of the inlet valves of the internal combustion engine and the valve train is controlled such that the cylinder specific deviations of the inlet valve lift are reduced or approach each other. 
     
     
       4. The method of  claim 1 , wherein the valve train of the internal combustion engine is configured for common control of the lift of the inlet valves of the internal combustion engine, and wherein the method further comprises:
 determining differences between the cylinder-specific deviations of the inlet valve lift are determined, and 
 determining a control variable for the minimum lift of the inlet valves to be set by the valve train base at least on the determined differences. 
 
     
     
       5. The method of  claim 1 , wherein the cylinder-specific deviations of the inlet valve lift are taken into account for cylinder-specific fuel delivery. 
     
     
       6. A control device for an internal combustion engine with a plurality of inlet valves and a device for varying the lift of the inlet valves, wherein the control device is programmed to control a variable valve train of an internal combustion engine with a plurality of cylinders by:
 determining an intake air quantity at a first operating point of the internal combustion engine, 
 at the first operating point, determining cylinder-specific values for a reduction of the fuel quantity by successively reducing the respective delivered quantity of fuel for each cylinder until a parameter representing the uneven running of the internal combustion engine has reached a specified uneven running limit value, 
 determining a ratio of a change of the inlet valve lift to a resulting change of the intake air quantity for the first operating point, 
 determining cylinder-specific deviations of the inlet valve lift from a valve reference value based on the ratio, the intake air quantity at the first operating point, and the associated fuel quantity reduction value, and 
 controlling the variable valve train based on at least one of the cylinder-specific deviations of the inlet valve lift. 
 
     
     
       7. The control device of  claim 6 , further programmed to:
 at a second operating point of the internal combustion engine, at which the inlet valve lift is greater than at the first operating point, determine other cylinder-specific values for a reduction of fuel quantity by successively reducing the respective quantity of fuel delivered for each cylinder until a parameter representing the uneven running of the internal combustion engine has reached a specified uneven running limit value, and 
 determine cylinder-specific errors in the fuel delivery based on the other cylinder-specific values for the reduction of fuel quantity and a fuel reference value, and 
 wherein the cylinder-specific errors in the fuel delivery are taken into account during determination of the cylinder-specific values of the reduction of the fuel quantity at the first operating point. 
 
     
     
       8. The control device of  claim 6 , wherein the valve train of the internal combustion engine is configured for cylinder-specific control of the lift of the inlet valves of the internal combustion engine and the valve train is controlled such that the cylinder specific deviations of the inlet valve lift are reduced or approach each other. 
     
     
       9. The control device of  claim 6 , wherein the valve train of the internal combustion engine is configured for common control of the lift of the inlet valves of the internal combustion engine, and wherein the control device is further programmed to:
 determine differences between the cylinder-specific deviations of the inlet valve lift are determined, and 
 determine a control variable for the minimum lift of the inlet valves to be set by the valve train based at least on the determined differences. 
 
     
     
       10. The control device of  claim 6 , wherein the cylinder-specific deviations of the inlet valve lift are taken into account for cylinder-specific fuel delivery.